Studies published nearly a decade ago reported that up to 34% of adult dogs and 35% of adult cats in the United States were overweight or obese.1,2 Prevalence among studies has differed; however, a more recent study reported that 63% of cats are overweight or obese.3 Not surprisingly, many studies have offered evidence of the detrimental consequences of excess weight in pets.1-3

Although not all clinical signs are overt, being overweight has been associated with many conditions that put a patients health at risk. Most data show only an association between obesity and disease, rather than direct causation; however, as evidence accumulates on the correlation between excess weight and disease, it is fair to assume that being lean is healthier.

Dogs

1. Poor quality & quantity of lifeSome of the most compelling evidence that obesity is harmful to the quality and quantity of life in pet dogs is easy to relay to owners. A lifetime study of Labrador retrievers found that dogs with an ideal body condition score (BCS) of 4/9 to 5/9 lived a median of 1.8 years longer than their slightly overweight counterparts with a BCS of 6/9 to 7/9.4 The slimmer dogs also had delayed onset of chronic illnesses.

Although some owners have expressed guilt or fear about depriving food as a rationale for not initiating weight loss plans, one study has shown decreased quality of life when pets are overweight and improvement in quality-of-life measures (eg, vitality, emotional disturbance, pain) after successful weight loss.5 Discussing the deleterious consequences of obesity and the benefits of weight loss may help alleviate owner concerns regarding weight management plans.

2. OsteoarthritisOne heavily studied disease process associated with the mechanical and functional effects of obesity is osteoarthritis. Maintaining an ideal weight has proven benefits in the prevention and treatment of this debilitating condition.

In a lifetime study of Labrador retrievers, leaner dogs had delayed onset of osteoarthritis as compared with their overweight counterparts.4 Although the mechanism is not completely understood, many have speculated that merely increasing physical force on the joint in overweight dogs would cause sufficient joint stress to result in osteoarthritis. Other theories have suggested that the proinflammatory nature of adipose tissue may cause an inflammatory and painful state within the joint.6 Regardless of cause, however, lameness and pain in dogs can be alleviated with weight loss. As little as 6% to 8% loss of total body weight has led to significant decreases in subjective and objective lameness scores.7

3. Intervertebral disk diseaseWeight management is strongly recommended in dogs predisposed to intervertebral disk disease (IVDD). Recommendations were previously based on anecdotal evidence, with the assumption that excess weight may cause additional stress on calcified disks and increase the risk for disk extrusion. One study of 700 dogs showed that obese dogs of all breeds were at increased risk for IVDD; but even being moderately overweight increased the risk in high-risk breeds (particularly the miniature dachshund [Figure 1]).8 In another study, dogs that underwent surgery for IVDD were 7.62 times more likely to be ambulating without assistance at the initial 3- to 4-week follow-up if they had a BCS of 6/9 or less.9

4. Subclinical conditionsIn dogs, obesity has been related to increased inflammatory mediators, hypercholesterolemia, hypertriglyceridemia, hyperinsulinemia, increased circulating leptin levels, and decreased circulating ghrelin levels.10,11 Because these endocrine-mediated changes may lead to such diseases as pancreatitis and diabetes, biochemistry panels are recommended in overweight pets without signs to monitor for abnormalities before diseases become apparent. In addition, because hypothyroidism is known to cause weight gain in dogs, thyroid levels should be checked routinely to rule out this disease. Of note, many overweight dogs have normal thyroid levels. Subclinical conditions can be challenging to discuss with owners of overweight pets because the consequences are not readily apparent; however, the ideal time to address weight management is before signs become evident.

5. Cardiorespiratory effectsObesity in dogs has been associated with various cardiac and respiratory conditions (although dogs are not at risk for coronary artery disease as are humans). Mild cardiac changes were noted in experimental studies of weight gain in dogs,12 and resting and recovery heart rates were also shown to be affected by BCS and exercise in pet dogs.13 Most notably, obesity has been linked to airway dysfunction14 and tracheal collapse.15 Although the exact benefits have not been studied, weight loss is considered part of the standard treatment for many respiratory conditions, including those previously listed, laryngeal paralysis, and others.

Cats

1. DiabetesIn cats, diabetes is the clinical consequence with the strongest correlation to obesity. Not only is obesity a risk factor for diabetes,16 but weight loss is a mainstay of treatment for diabetic cats and increases the likelihood of remission.17,18 Because significant endocrine-mediated changes can be evident on laboratory screening before clinical disease is apparent, biochemistry panels (looking for hyperglycemia and altered lipid profiles) are routinely recommended for any overweight cat. Insulin sensitivity can decrease with obesity, and glucose tolerance and lipid profiles can be altered in cats with excess weight.19-21 Such impaired insulin sensitivity has been associated with obesity, even in cats younger than 1 year of age,22 highlighting the need for preventive and aggressive weight management.

2. Urinary diseaseObesity reportedly plays a role in the feline urinary system. Obesity has been shown to be a risk factor for feline lower urinary tract disease,2 and weight lossalong with dietary and stress managementis considered part of potential treatment strategies for feline urolithiasis.23 Although further studies in cats are warranted, obesity in dogs has also been linked to functional and structural changes in the kidneys, suggesting that obesity may be a potential risk factor for renal disease as well in other companion animals.24,25 Encouraging physical activity and environmental enrichment may help cats maintain a healthy weight and reduce the risk for lower urinary tract disease.

3. OsteoarthritisSimilar to osteoarthritis in dogs, osteoarthritis in cats is believed to be associated with obesity. Maintaining an ideal body weight has shown benefits in preventing and treating osteoarthritis in many species. Compared with lean cats, heavy cats were almost three times more likely to present for lameness not associated with bite trauma.16 In addition, obese cats were almost five times as likely to develop lameness that required veterinary care.16 As in dogs, the mechanism is not completely understood but may be related to increased physical force causing stress on joints. Other theories have suggested that the proinflammatory nature of adipose tissue may induce pain and inflammation in the joint space.6

4. Subclinical conditionsStudies in humans and other animals have shown the important role of adipose tissue in maintaining healthy weight. As an individual becomes heavier, adipose tissue increases the production of hormones and inflammatory mediators (eg, adipokines [leptin]) that can have considerable clinical and subclinical effects on the body.10 These effects can predispose to or exacerbate diseases through a proinflammatory process (ie, adipose tissue producing inflammatory cytokines [tumor necrosis factor-, interleukin-6]).10,26 In cats, hypothyroidism is rare and usually only seen as a result of iatrogenic overtreatment of hyperthyroidism. However, many subclinical changes that occur in overweight cats can be assessed on biochemistry panels before clinical disease becomes apparent (eg, hyperglycemia, hyperlipidemia).19-21 Subclinical conditions can be difficult to discuss with owners, but diabetes in particular is best diagnosed early in cats, as prevention is easier than treatment.

5. Poor quality & quantity of lifeEvidence has shown that obesity can be harmful to cats with regard to quality and quantity of life. Although anecdotal, evidence from canine studies can be extrapolated to cats. Like dogs, cats with an ideal BCS are likely to live longer and have a better overall quality of life than their overweight counterparts.4 Likewise, owners may have feelings of guilt or fear about depriving their cats of food as rationale for not initiating weight loss.5 Discussing the potentially severe consequences of obesity and the benefits of weight loss for improving quality of life and alleviating pain and suffering may help lessen owner concerns about implementing weight management.

Closing thoughts

Even if signs are not apparent, obese patients reportedly have higher anesthetic risks and medical costs and require special consideration when dosing medications with narrow safety ranges.27,28 Excess weight is easier to prevent than treat, so conveying the urgency of weight management before consequences are apparent can help keep patients healthier and happier.

DEBORAH LINDER, DVM, DACVN, is head of Tufts Obesity Clinic for Animals and volunteers with Tufts Paws for People Animal Visitation Group. Her interests include obesity management and client education. Dr. Linders research investigates safe and effective weight loss strategies for pets and the effects of obesity on animal well-being. Dr. Linder earned her DVM from Tufts Cummings.

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